A polygraph (popularly referred to as a lie detector) is an instrument that measures and records several physiological responses such as blood pressure, pulse, respiration, breathing rhythms, body temperature and skin conductivity while the subject is asked and answers a series of questions, on the theory that false answers will produce distinctive measurements. The polygraph measures physiological changes caused by the sympathetic nervous system during questioning. Within the US federal government, a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination.

Polygraphs are in some countries used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. The use and effectiveness of the polygraph is controversial, with the manner of its use and its validity subject to increasing criticism.

Several devices similar to Keeler's polygraph version included the Berkeley Psychograph, a blood pressure-pulse-respiration recorder developed by C. D. Lee in 1936[3] and the Darrow Behavior Research Photopolygraph, which was developed and intended solely for behavior research experiments[4][5]

Makenzie wrote a second paper on the concept in 1915, when finishing his undergraduate studies. He entered Harvard Law School and graduated in 1918, re-publishing his earlier work in 1917.[6] According to their son, Marston's wife, Elizabeth Holloway Marston, was also involved in the development of the systolic blood-pressure test: "According to Marston’s son, it was his mother Elizabeth, Marston’s wife, who suggested to him that 'When she got mad or excited, her blood pressure seemed to climb' (Lamb, 2001). Although Elizabeth is not listed as Marston’s collaborator in his early work, Lamb, Matte (1996), and others refer directly and indirectly to Elizabeth’s work on her husband’s deception research. She also appears in a picture taken in his polygraph laboratory in the 1920s (reproduced in Marston, 1938)."[7][8] The comic book character, Wonder Woman by William Marston (and influenced by Elizabeth Marston[9][10] ) carries a magic lasso which was modelled upon the pneumograph (breathing monitor) test.[11][9]

Marston was the self proclaimed “father of the polygraph” despite his predecessor's contributions.
Marston remained the device's primary advocate, lobbying for its use in the courts. In 1938 he published a book, The Lie Detector Test, wherein he documented the theory and use of the device.[12] In 1938 he appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.[13][14][15]

A device which recorded muscular activity accompanying changes in blood pressure was developed in 1945 by John E. Reid, who claimed that greater accuracy could be obtained by making these recordings simultaneously with standard blood pressure-pulse-respiration recordings.[16][17]